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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Applications of Continuous Wave Free Precession Sequences in Low-Field, Time-Domain NMR

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Moraes, Tiago Bueno [1] ; Monaretto, Tatiana [2] ; Colnago, Luiz Alberto [3]
Total Authors: 3
[1] Univ Fed Sao Carlos, Dept Fis, UFSCar, Rod Washington Luis, Km 235, BR-13565905 Sao Carlos, SP - Brazil
[2] Univ Sao Paulo, Inst Quim Sao Carlos, Ave Trabalhador Sao Carlense 400, BR-13566590 Sao Carlos, SP - Brazil
[3] Embrapa Instrumentacao, Rua 15 Novembro 1452, BR-13560970 Sao Carlos, SP - Brazil
Total Affiliations: 3
Document type: Review article
Source: APPLIED SCIENCES-BASEL; v. 9, n. 7 APR 1 2019.
Web of Science Citations: 0

This review discusses the theory and applications of the Continuous Wave Free Precession (CWFP) sequence in low-field, time-domain nuclear magnetic resonance (TD-NMR). CWFP is a special case of the Steady State Free Precession (SSFP) regime that is obtained when a train of radiofrequency pulses, separated by a time interval T-p shorter than the effective transverse relaxation time (T-2{*}), is applied to a sample. Unlike regular pulsed experiments, in the CWFP regime, the amplitude is not dependent on T-1. Therefore, T-p should be as short as possible (limited by hardware). For T-p < 0.5 ms, thousands of scans can be performed per second, and the signal to noise ratio can be enhanced by more than one order of magnitude. The amplitude of the CWFP signal is dependent on T-1/T-2; therefore, it can be used in quantitative analyses for samples with a similar relaxation ratio. The time constant to reach the CWFP regime (T{*}) is also dependent on relaxation times and flip angle (). Therefore, T{*} has been used as a single shot experiment to measure T-1 using a low flip angle (5 degrees) or T-2, using = 180 degrees. For measuring T-1 and T-2 simultaneously in a single experiment, it is necessary to use = 90 degrees, the values of T{*} and M-0, and the magnitude of CWFP signal |M-ss|. Therefore, CWFP is an important sequence for TD-NMR, being an alternative to the Carr-Purcell-Meiboom-Gill sequence, which depends only on T-2. The use of CWFP for the improvement of the signal to noise ratio in quantitative and qualitative analyses and in relaxation measurements are presented and discussed. (AU)

FAPESP's process: 13/03770-1 - Development and applications of pulses sequences with alternating phases in the time domain NMR
Grantee:Tatiana Monaretto
Support type: Scholarships in Brazil - Master
FAPESP's process: 14/22126-9 - Development of time domain NMR spectrometers and methods for chemical analyses in field
Grantee:Luiz Alberto Colnago
Support type: Regular Research Grants
FAPESP's process: 17/12864-0 - Effect of NMR magnetic field in chemical reactions monitored NMR in situ
Grantee:Luiz Alberto Colnago
Support type: Regular Research Grants
FAPESP's process: 14/16952-3 - Development of fast NMR methods for product and process monitoring using compact low-field systems
Grantee:Tiago Bueno de Moraes
Support type: Scholarships abroad - Research Internship - Doctorate